For words that have only 3 letters, there is not any 4th letter. One example is with the word “include”, there are no more letters afterwards and therefore need to be the word "increase". The word “addict” is in the BIP39 wordlist however you might have made use of “addi” https://socialrus.com/story18294440/new-step-by-step-map-for-ledger-seed-phrase-bip39